1. Field of the Invention
The present invention generally relates to an arbitration method of a bus bridge and, more particularly, to an arbitration method performed by a bus bridge such as a PCI—PCI bridge of personal computers, a PCI-card bus bridge, a PCI-IEEE1394 (OHCI-Link) bridge, etc.
2. Description of the Related Art
The performance of computers has been accelerated every year, and peripheral devices such as memory devices are sped up and upgraded. The interface used for the computers and the peripheral devices includes the IEEE1394 interface. The IEEE1394 interface is standardized as a high-speed serial bus for the next generation's multimedia by IEEE, which can be extended over the consumer and the computer.
In the IEEE1394 standard, a data transfer rate from 100 Mbps to 400 Mbps is used. The IEEE1394 allows use of an isochronous transfer so as to guarantee a real-time operation using the isochronous transfer. That is, because the priority right is assigned each 125 μs in the isochronous transfer of IEEE1394, the real time operation for the data transfer can be guaranteed.
The above-mentioned IEEE-1394 standard is not for I/O devices but for buses. When the IEEE-1394 standard is used for a system, a bus bridge is provided so as to interface a primary side bus with a secondary side bus, the primary side bus being a local bus in the system.
There might be a case in which only a limited number of bus bridges can be provided in a system, and the number of buses to be connected in the system is greater than the limited number of bus bridges. In such a case, two or more buses may be connected to a single bus bridge by adding a unique ID to each of the buses.
There is a bridge device that interfaces a primary side bus, which is a local bus in the system, with a secondary side bus. Such a bridge device may supports different operations with respect to the bus control. For instance, one of the operations relates to the serial bus according to the IEEE1394 standard and the other operation relates to the bus according to a standard other than the IEEE1394 standard.
When the bus in accordance with the IEEE1394 standard begins accessing the primary side bus, it takes a relatively long time to transfer data. Therefore, the IEEE1394 bus occupies the access right. Moreover, when arbitration is performed, the access right might not be handed over to other secondary side buses when priority is given to the IEEE1394 side.